contrib/dockerdeb

selectors2: do not use platform.system()

`platform.system()` may have a side effect spawning a shell executing
`uname -p`, which may print a warning when the current directory is removed:

  shell-init: error retrieving current directory: getcwd: cannot access parent directories: No such file or directory

This patch changes selectors2 to test the `sys.platform` string, which is a
much safer way to detect Jython.

Jython's `sys.platform` looks like this:

  Jython 2.7.1 (default:0df7adb1b397, Jun 30 2017, 19:02:43)
  [OpenJDK 64-Bit Server VM (Oracle Corporation)] on java1.8.0_144
  Type "help", "copyright", "credits" or "license" for more information.
  >>> import sys
  >>> sys.platform
  'java1.8.0_144 ( ==linux2 for targets )'

Differential Revision: https://phab.mercurial-scm.org/D1018

#!/bin/bash -eu

. $(dirname $0)/dockerlib.sh
. $(dirname $0)/packagelib.sh

BUILDDIR=$(dirname $0)
export ROOTDIR=$(cd $BUILDDIR/.. > /dev/null; pwd)

checkdocker

DISTID="$1"
CODENAME="$2"
PLATFORM="$1-$2"
shift; shift # extra params are passed to build process

OUTPUTDIR=${OUTPUTDIR:=$ROOTDIR/packages/$PLATFORM}

initcontainer $PLATFORM

# debuild only appears to be able to save built debs etc to .., so we
# have to share the .. of the current directory with the docker
# container and hope it's writable. Whee.
dn=$(basename $PWD)

if [ $(uname) = "Darwin" ] ; then
    $DOCKER run -u $DBUILDUSER --rm -v $PWD/..:/mnt $CONTAINER \
            sh -c "cd /mnt/$dn && make clean && make local"
fi
$DOCKER run -u $DBUILDUSER --rm -v $PWD/..:/mnt $CONTAINER \
  sh -c "cd /mnt/$dn && DEB_BUILD_OPTIONS='${DEB_BUILD_OPTIONS:=}' contrib/builddeb --build --distid $DISTID --codename $CODENAME $@"
contrib/builddeb --cleanup --distid $DISTID --codename $CODENAME
if [ $(uname) = "Darwin" ] ; then
    $DOCKER run -u $DBUILDUSER --rm -v $PWD/..:/mnt $CONTAINER \
            sh -c "cd /mnt/$dn && make clean"
fi